Legal action has been threatened by the Democratic Unionist Party over the decision to restrict the flying of the Union flag as pressure grew for violent protests to stop.

One of Northern Ireland's most senior Protestant ministers called on loyalists to end "intolerable" attacks on police.

They followed Belfast City Council's vote to hoist the emblem at City Hall only on designated days like royal birthdays.

The Flag was flown last week for the Duchess of Cambridge's birthday

Officers have been pelted with bricks, petrol bombs and other missiles, leaving dozens injured.

Unionist politicians tried to find common ground within a community forum considering ways to move beyond demonstrations but insisted it was not a step towards a single unionist party.

Presbyterian Moderator Dr Roy Patton said: "The situation being faced by the police is intolerable and in keeping order on our streets and bringing people before the courts the PSNI (Police Service of Northern Ireland) must have the full support of all who want to see an end to this violence."

There have been nearly 40 days of protests over the council's decision to fly the flag on 18 designated days.

The DUP group on the council claimed the change breached the organisation's equality scheme and made a formal complaint.

Group secretary John Hussey said: "The DUP is committed to pursuing all political avenues to overturning the disastrous decision by Sinn Fein, SDLP and the Alliance party and to repairing the harm to good relations and a shared future it has caused."

Until last month, the flag flew every day of the year from the City Hall. Disputes over flags and symbols have been a regular occurrence in Northern Ireland and the restrictions sparked some of the most sustained unrest since the signing of the Good Friday Agreement in 1998.

Despite weeks of flag-waving pickets and road blocks in parts of Belfast, some producing full-scale riots with 66 officers hurt, councillors have vowed not to reverse their decision.

The Alliance Party, which controls the balance of power, has said the designated days option was in line with a recommendation from Northern Ireland's Equality Commission as an approach which would promote good relations between nationalists and unionists.

Loyalists protesting the restrictions on the flying of the flag

A Belfast City Council spokeswoman said: "The decision to introduce the policy of flying the Union flag at City Hall was taken democratically by elected members at the monthly meeting of Belfast City Council on December 3.

"The council has taken legal advice throughout this process and the decision is in keeping with the outcome of the equality impact assessment that was undertaken in line with the advice of the Equality Commission.

"The designated days agreed are in keeping with those notified by the UK Government's Department of Culture, Media and Sport."

The first meeting of a Unionist Forum co-chaired by Ulster Unionist leader Mike Nesbitt and Democratic Unionist First Minister Peter Robinson was held this week to discuss ways of ending the trouble and empowering the working-class east Belfast community where violence has been fiercest.

Mr Nesbitt said: "It is not the first step on the road to unionist unity. Nor is it a vehicle that will drive us to the creation of a single monolithic unionist party.

"Rather, it is a response to the cry, heard loudest in Belfast, for leadership and cohesion from the Ulster Unionist Party and others with political mandates."

A series of roads in Belfast were closed tonight due to another round of flag protests.

Access to Ravenhill rugby ground in the city was also limited as a result of demonstrations, with thousands of supporters encountering delays as they tried to make their way to Ulster Rugby's crunch Heineken Cup tie with Glasgow.

Routes in Bangor and Newtownards were also blocked by pickets.

Police tonight came under attack during disorder in Newtownabbey just north of Belfast.

Officers were pelted with petrol bombs, fireworks and other missiles in the outbreak of trouble at the O'Neill Road roundabout.